During wash and rinse cycles, dishwashers typically circulate a fluid through the wash chamber and over articles such as pots, pans, silverware, and other cooking utensils. The fluid can be e.g., various combinations of water and detergent during the wash cycle or water (which may include additives) during the rinse cycle. Typically the fluid is recirculated during a given cycle using a pump. Fluid is collected at or near the bottom of the wash chamber and pumped back into the chamber through e.g., nozzles in the spray arms and other openings that direct the fluid against the articles to be cleaned or rinsed.
Depending upon the level of soil upon the articles, the fluid will become contaminated with the soil in the form of debris and particles that are carried with the fluid. In order to protect the pump and make sure the fluid can continue to recirculate through the wash chamber, the fluid is typically filtered during its movement between the wash chamber and the pump so that relatively clean fluid is supplied to the pump inlet. In addition to pump protection, such filtration also helps to clean the articles by removing soil from the fluid.
During the overall cleaning process, larger soil particles are typically present at the beginning of the process. As soil is removed by filtration of the fluid between the wash chamber and the pump during recirculation, the amount and size of particles in the recirculated fluid will decrease. Accordingly, generally the amount and size of particles carried by the fluid will be smaller towards e.g., the end of the wash cycle and can be even smaller towards the end of the rinse cycle.
For mechanical filtration, the selectivity of the filter to remove soil particles of different sizes is typically determined by providing fluid paths (such as pores or apertures) in the filter that are smaller than the particles for which filtration is desired. Particles having a dimension larger than the width of the fluid paths will be prevented from passing through the filter while particles smaller than the width of the fluid path will generally pass through. While a filter capable of capturing a majority of both the larger and smaller soil particles could be used throughout the entire cleaning process by using a small pore filter (e.g., a fine filter), such would come at an increased pressure drop as both large and small soil particles would become entrained in the filter from the beginning of the cleaning cycle. The filter could even become completely clogged and/or increased energy may be required to move fluid through the filter. A filter having larger pores can be used (e.g., a coarse filter) and less pressure drop would be expected, but smaller soil particles will generally pass through and remain in the fluid to negatively impact the cleaning process.
Accordingly, a filter system for a dishwasher would be beneficial. More specifically, a filter system for a dishwasher that can provide for effective filtration of both large and small particles during the entire cleaning process would be useful. Such a filter system that can change the amount of flow between different filters during the cleaning process so that both coarse and fine filters may be used at different stages of the cleaning cycle would be particularly beneficial.